The present invention relates to a gas discharge switch and more particularly to such a switch with a low-pressure gas discharge segment which is provided with an anode and at least one main cathode and arranged in an ionizable working gas and to which a control device which contains a cathode is assigned.
The ignition voltage for a predetermined gas discharge segment and its usual graphic representation as a function of the product of the gas pressure p and the electrode distance D in the ignition characteristic curve is known to be formed by taking the ignition probability, an important aid in characterizing electric discharge apparatus, into consideration. In the determination of the electric voltage resistance of the preset gas discharge segment, an infinitely large plate capacitor and its ignition characteristic curve are generally used for a comparison. However, the practical embodiment of such discharge segments has electrodes with finite dimensions. While it is sufficient, in order to determine the right branch of the ignition characteristic curve known as the Paschen curve (i.e., in order to study the so-called far breakdown zone, including the voltage minimum), merely to arrange two flat, rounded-off plates, possibly provided with a so-called Rogowski profile at the edges, parallel to one another, such a design arrangement is not usable to study ignition characteristic lines in the left part of the Paschen curve, i.e., in the so-called post breakdown zone, because then indirect charges can occur. Such indirect discharges can be avoided with an electrode design with flat plate electrodes which are arranged coaxial to one another, and are bent away from one another at their edges, with a small radius of curvature relative to the electrode distance, and guided along the inside cylindrical insulator surface. In this way, a gap is always formed between the bent-away, cylinder-shaped edge zone of the electrodes and the inside wall of the hollow cylinder insulator. Such embodiments of low-pressure gas discharge segments are also suitable for the near breakdown zone.
Low-pressure gas discharge segments are known to be suitable as switches for high currents, for example of about 50 kA to 2 MA, and high voltages up to about 100 kV. These gas discharge switches work with a pressure of the working gas, preferably hydrogen, of less than 1 torr at an electrode gap of less than 1 cm, with a voltage about 10 kV in the left branch of the Paschen curve. Since these switches can only turn a current on, but not off again, they are particularly suited for discharging large capacitors, for example at a voltage of 10 to 100 Kv and currents up to 10 MA, at which several switches are then generally switched in parallel. The discharge switch contains an anode and a main cathode, which are arranged coaxial to one another and are separated at the edge by a ring-shaped insulator (Proc. IEE, Volume 111, Number 1, January 1964, pages 203 to 213).
Such gas discharge switches can be controlled by a pulsed low-pressure gas discharge. The main discharge is initiated by a hollow cathode discharge and ignited by injection of charge carriers. For this purpose, a control device is provided, which contains a cage provided with holes, which surrounds the rear space of the cathode. The discharge segment is separated from the zone of a preionization discharge, which is a flow discharge, by the cage. Between the cage and the zone of the glow discharge, various auxiliary electrodes for shielding and potential control can also be provided as disclosed in Sci. Instr. 19 (1986), The Inst. of Physics, Great Britain, pages 466 to 470.
In this closed system, the pressure of the working gas decreases with an increasing number of switching processes. The reason for this lies in the implantation of charged high-energy particles during the discharge. In order to counteract this, the gas discharge system can be provided with a gas storage for the working gas, which can consist of a metal suitable as a storage or reservoir, for example titanium, zirconium, tantalum, palladium or even lanthane. Furthermore, intermetallic cubic Laves phases, which consist of a compound of iron hydride with one of the rare earth elements are suitable as storage material. This storage material absorbs gas, at a raised temperature, in an atmosphere enriched with the working gas, and this gas is stored in the lattice. In a vacuum or in the working gas of a gas discharge switch, it gives the working gas off again when heated.
To regulate the working gas to a constant pressure, a gas storage with an automatic pressure control can be provided. A known embodiment of such a gas storage consists of two generators, one of which serves as a storage and the other of which serves as a getter. The generator gives off gas when heated, for example by a heating coil, and the storage absorbs gas if too much gas is released and therefore a pressure increase occurs. The distance between the storage metal and the generator sheath is selected so it is not greater than the mean free path length of the working gas, i.e., at most approximately 0.4 mm for hydrogen as disclosed in Sov. Phys. Tech. Phys. Volume 21, Number 4, April 1976, pages 487 to 489.